Compositions and methods for planarizing or polishing the surface of a substrate are well known in the art. Polishing compositions (also known as polishing slurries) typically contain an abrasive material in an aqueous solution and are applied to a surface by contacting the surface with a polishing pad saturated with the polishing composition. Typical abrasive materials include silicon dioxide, cerium oxide, aluminum oxide, zirconium oxide, and tin oxide. U.S. Pat. No. 5,527,423, for example, describes a method for chemically-mechanically polishing a metal layer by contacting the surface with a polishing slurry comprising high purity fine metal oxide particles in an aqueous medium. The polishing slurry is typically used in conjunction with a polishing pad (e.g., polishing cloth or disk). Suitable polishing pads are described in U.S. Pat. Nos. 6,062,968, 6,117,000, and 6,126,532, which disclose the use of sintered polyurethane polishing pads having an open-celled porous network, and U.S. Pat. No. 5,489,233, which discloses the use of solid polishing pads having a surface texture or pattern. Alternatively, the abrasive material may be incorporated into the polishing pad. U.S. Pat. No. 5,958,794 discloses a fixed abrasive polishing pad.
Conventional polishing systems and polishing methods typically are not entirely satisfactory at planarizing semiconductor wafers. In particular, polishing compositions and polishing pads can have less than desirable polishing rates or polishing selectivities, and their use in chemically-mechanically polishing semiconductor surfaces can result in poor surface quality. Because the performance of a semiconductor wafer is directly associated with the planarity of its surface, it is crucial to use a polishing composition and method that results in a high polishing efficiency, selectivity, uniformity, and removal rate and leaves a high quality polish with minimal surface defects.
The difficulty in creating an effective polishing system for semiconductor wafers stems from the complexity of the semiconductor wafer. Semiconductor wafers are typically composed of a substrate, on which a plurality of transistors has been formed. Integrated circuits are chemically and physically connected into a substrate by patterning regions in the substrate and layers on the substrate. To produce an operable semiconductor wafer and to maximize the yield, performance, and reliability of the wafer, it is desirable to polish select surfaces of the wafer without adversely affecting underlying structures or topography. In fact, various problems in semiconductor fabrication can occur if the process steps are not performed on wafer surfaces that are adequately planarized.
Typically, polishing compositions for polishing dielectric materials require an alkaline pH in order to obtain sufficient removal rates for the dielectric. For example, U.S. Pat. Nos. 4,169,337, 4,462,188, and 4,867,757 disclose polishing compositions for silicon dioxide removal comprising silica abrasives at an alkaline pH. Similarly, WO 00/25984, WO 01/56070, and WO 02/01620 disclose polishing compositions for Shallow Trench Isolation (STI) polishing comprising fumed silica at alkaline pH. EP 853 110 A1 describes a polishing composition having a pH of 11–13, which purportedly increase selectivity in STI polishing. U.S. Patent Application Publication 2001/0051433 A1 discloses a polishing composition for dielectric chemical-mechanical polishing (CMP) comprising filmed silica and a cesium salt with a pH of 7 or greater. Such alkaline polishing compositions, while effective in the removal of silicon dioxide dielectric materials, provide poor selectivity in substrates comprising both silicon dioxide and silicon nitride layers, as in STI substrates. The use of chelating acid additives to improve the selectivity in STI polishing is known in the art. For example, U.S. Pat. Nos. 5,738,800, 6,042,741, 6,132,637, and 6,218,305 disclose the use of acid-containing complexing agents in polishing compositions comprising an abrasive (e.g., ceria or silica). U.S. Pat. No. 5,614,444 discloses the use of chemical additives comprising anionic, cationic, or nonionic polar groups and apolar organic components to suppress the removal of a dielectric material. EP 1 061 111 A1 discloses polishing compositions for STI polishing comprising ceria abrasive and an organic compound comprising a carboxylic acid or sulfonic acid group.
A need remains, however, for polishing systems and polishing methods that will exhibit desirable planarization efficiency, selectivity, uniformity, and removal rate during the polishing and planarization of dielectric substrates, while minimizing defectivity, such as surface imperfections and damage to underlying structures and topography during polishing and planarization. The invention seeks to provide such a chemical-mechanical polishing system and method. These and other advantages of the invention will be apparent from the description of the invention provided herein.